Internal Combustion engines historically have been started, or brought into an operating state, by a manual forced rotation of the crankshaft which engages the elements of the engine to begin its four stroke combustion cycle. Early engines accomplished this using a hand crank. More recently electric motors have been serving this purpose.
To develop sufficient torque to overcome angular inertia and attain initial rotation, significant currents are needed since the mass to be rotated is that of the engine's key components—not to mention that closed cylinders cause compressive opposition to the rotation of the crankshaft due to the motion of the pistons in the closed cylinders. A rule of thumb is that it takes one ampere for every cubic inch of displacement of engine size to successfully start an engine. This means that, for typical engines of today, it is not unusual for the starting process to require hundreds of amperes over a time span anywhere from 10 ms to over 1 second. Since automobiles use a relatively low voltage, e.g. 12V, developing and transporting these large currents depends on a low resistance pathways, since ohm's law states that:
  Current  =      Voltage    Resistance  
Devices like electric battery jump starters are typically attached to vehicle batteries simply and quickly by placing clamps onto the battery terminals, or on the positive terminal and the vehicle chassis. The quality of the connection (as measured by the resistivity of the connection) can determine the success of the jump-starting operation by either facilitating a parallel boost from the jump starter when the connection has sufficiently low resistance, or negating the benefit of the jump starter in the case of a poor connection (high resistance).
Knowing the resistance of the connection benefits the jump starting process by allowing the user to optimize the connection, thus maximizing the chances of a successful jump start.